Planck Density. Something to get your head around.

So last week’s New Scientist attempted to familiarise me with the concept of  ‘loop quantum cosmology’. If I get this right (and please, somebody correct me if I am wrong) this theory states that before the big bang our universe already existed: after expanding to its fullest diameter it then shrank back until it reached microscopic volume in which things were pretty dense: 5.1 × 1096 kilograms per cubic metre dense (also called Planck Density) . Now that is even denser than population density in the East End. So when the universe reached that state of density, every thing started anew with a ‘big bounce’.

That of course means that we are all recycled, like a park bench made ouf recycled plastic.  A comforting thought, but the creationists will probably have another hissy fit when they find out (again) that the universe is older that 6000 years.


5 comments

  1. I wanted to know how big the universe was when it was at the Planck density stage, which I gather would be one Planck second after the Big Bang. I used the known size of the universe and the average density of matter in the universe to calculate the mass of the universe. The problem is that these are rather debatable points. Depending on whether dark matter is included the answer varies by a factor of 50 million. However it is still a very, very small part of a cubic millimetre.

    • Well since the visible universe is about 10^23 solar masses at planck density all that can fit inside a proton (10^-15m in diameter). Thing is we don’t know what’s beyond our horizon that we can’t see, if anything. Extrapolating from Inflation theory what we can see is only 1 part in 10^26 of all of it. At face value then at planck density that’s about .5 microns = still less than 1/10 the size of a red blood cell.

  2. “A comforting thought, but the creationists will probably have another hissy fit when they find out (again) that the universe is older that 6000 years.”

    Not really. Remember time is relative to the observer, and when we’re talking about an entity that claims to have invented time/space matter/energy, it isn’t safe to assume he’s bound by the same definition (note that time for the first 6 days is described differently and uniquely than the human years that follow). “6000 years” is no stumbling block for an educated Christian (though all Christians are routinely stereotyped as uneducated).

    Also, LQC doesn’t seem to promise to give us the answer to “where did time/space matter/energy come from in the first place?” In no way does it seem to inconvenience the concept of a conciousness beyond the universe responsible for it’s existence and fundamental laws. Folks looking for proof or disproof of God by scientific standards are really barking up the wrong tree. One might as well make absolute statements about the health or lack thereof of Schrodenger’s cat while it’s still in the box (You’ll find out when it’s opened)

    LCQ is an interesting theory, and it will be fascinating to watch it’s progress.

  3. Hold your horses on anything related to QT; Cosmology is on the cusp of realizing that The Vacuum doesn’t and never has existed and, once that realization sinks in, QT will lose both the Photon and particle/wave duality (gutting QT) and Theoretical Physics will turn into Huxley sputtering about the Steady State Universe.


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